Let it all out: Casey Affleck with Lucas Hedges in Manchester by the Sea.
Photograph: Claire Folger

The time-honoured story of emotion goes something like this: we all have emotions built in from birth. They are distinct, recognisable phenomena inside us. When something happens in the world, whether it’s a gunshot or a flirtatious glance, our emotions come on quickly and automatically, as if someone has flipped a switch.

Modern science has an account that fits this story, which I call the classical view of emotion. According to this view, we have many emotional circuits in our brains, and each is said to cause a distinct set of changes – that is, a fingerprint. Perhaps an annoying co-worker triggers your “anger neurons”, so your blood pressure rises – you scowl, yell and feel the heat of fury. Or an alarming news story triggers your “fear neurons”, so your heart races – you freeze and feel a flash of dread.

Emotions are thought to be a kind of brute reflex, very often at odds with our rationality. This internal battle between emotion and reason is one of the great narratives of western civilisation. It helps define you as human. Without rationality, you are merely an emotional beast. This view of emotions has been around for millennia. Plato believed a version of it. So did Hippocrates, Aristotle, the Buddha, René Descartes, Sigmund Freud and Charles Darwin. Today, prominent thinkers such as Steven Pinker, Paul Ekman and the Dalai Lama also offer up descriptions of emotions rooted in the classical view.

Scientific research has not revealed a consistent, physical fingerprint for even a single emotion

And yet there is abundant scientific evidence that this view cannot possibly be true. Research has not revealed a consistent, physical fingerprint for even a single emotion. When scientists attach electrodes to a person’s face and measure muscle movement during an emotion, they find tremendous variety, not uniformity. They find the same variety with the body and brain. You can experience anger with or without a spike in blood pressure. You can experience fear with or without a change in the amygdala, the brain region tagged as the home of fear.

When scientists set aside the classical view and just look at the data, a radically different explanation for emotion comes to light. We find that emotions are not universal but vary from culture to culture. They are not triggered; you create them. They emerge as a combination of the physical properties of your body, a flexible brain that wires itself to whatever environment it develops in, and your culture and upbringing.

Why should you care which theory of emotion is correct? Because belief in the classical view affects your life in ways you might not realise. Imagine you’re in a doctor’s surgery, complaining of chest pressure and shortness of breath, which may be symptoms of a heart attack. If you’re a woman, you’re more likely to be diagnosed with anxiety and sent home, whereas a man is more likely to be diagnosed with heart disease and receive preventive treatment. As a result, women over 65 die more frequently from heart attacks than men do. The perceptions of doctors, nurses and the patients themselves are shaped by classical view beliefs, including that women are inherently more emotional – with fatal consequences.

We are, I believe, in the midst of a revolution in our understanding of emotion, the mind and the brain – a revolution that may compel us to radically rethink our attitudes to mental and physical illness, our understanding of personal relationships, our approaches to raising children, and ultimately our view of ourselves.